Quantum mechanics, as a fundamental theory of physics, describes the behavior of particles and electromagnetic radiation, such as light, in terms of wave-particle duality. This means that particles like electrons and photons (which make up light) can exhibit both wave-like and particle-like properties depending on the experimental setup and observation.
The famous double-slit experiment is often used to illustrate this duality and provide evidence for the wave-like nature of light. In this experiment, a beam of light or a stream of particles (e.g., electrons) is directed at a barrier with two slits. Behind the barrier, a screen is placed to observe the pattern produced by the light or particles after passing through the slits.
When the experiment is performed with light, an interference pattern is observed on the screen, which is characteristic of waves. This pattern consists of alternating bright and dark regions resulting from the constructive and destructive interference of the light waves that pass through the slits. This behavior is consistent with the wave nature of light.
On the other hand, when the experiment is conducted with individual particles, such as electrons, they are detected on the screen as discrete points, creating a pattern that appears to be made up of individual particles. This outcome is consistent with the particle nature of electrons.
Further evidence supporting the wave-particle duality of light and matter comes from other experiments, such as the photoelectric effect and the Compton scattering experiment. The photoelectric effect demonstrates that light can behave as particles (photons) by liberating electrons from a material when the light energy exceeds a specific threshold. Compton scattering shows that light (X-rays or gamma rays) can also exhibit particle-like behavior when interacting with electrons, resulting in the scattering of photons at different angles.
In summary, quantum mechanics provides evidence for the wave-particle duality of light. It demonstrates that light can exhibit wave-like behavior (as observed in interference patterns) and particle-like behavior (as observed in the emission and absorption of photons and interactions with matter). The behavior of light is context-dependent, and the choice of experimental setup determines whether its wave or particle nature predominates.